Australiathe ""lukewarm, lilac unknown'' waters off the boot camp of Darwin and the saltbushes, paddocks and ``mottled wave'' of the remote home village of the Tregenza family on the southern peninsulais perhaps this fine novel's chief character as the country becomes less isolated and more modern in the wake of WW II. Jack Tregenza, chance survivor of the war, has raised his niece Penny after the wartime death of his brother Peter. This is a slim, unsentimental book about vivid people whose apparent ordinariness is deceptive. The deliberate discontinuity of the bookwhich opens with Penny's wedding and closes with Penny's conception and the parting of her unmarried parents after a single night together as Peter leaves for warrobs the story of narrative tension, but readers will be rewarded by a truthful family portrait and a multi-angled picture of a changing world, especially for women. Australian usages may occasionally distract American readers, but Peter's plea, ``Jack, breathe!'' as he labors to save his brother when they both find themselves struggling for life in a military hospital speaks from the heart to everyone. (May)